More resolving via IPv6 / 2017-07-15

I was reading Debian Stretch - Het Lab Henk van de Kamer (in Dutch) which mentions removing package rdnssd to avoid a dependency problem. But I like rdnssd as it helps use the nameservers available via IPv6 in a network with only SLAAC and no DHCPv6.

Right away I had to check on my own laptop with Ubuntu 16.04 and noticed all traffic was going to the IPv4 address of the local resolver. Which is not what I want, I want to prefer IPv6 when possible. Searching found Bug #936712 “NetworkManager should put IPv6 DNS servers before I...” : Bugs : network-manager package : Ubuntu which is indeed what I saw, and it's still showing in Ubuntu 16.04 Xenial.

My solution was to stop using dnsmasq, and switch to a generated resolv.conf from NetworkManager. To do that I had to update /etc/NetworkManager/NetworkManager.conf to have:

#dns=dnsmasq
dns=none
rc-manager=file

And now I have a resolv.conf with only 3 IPv6 nameservers and no search domains. Not exactly what I want, but at least IPv6 is preferred. I considered something using only the first three resolvers because that is a maximum somewhere but just advertising two resolvers via radvd also makes two show up in the generated resolv.conf. This is not perfect. The generated resolv.conf has comments that it is generated by resolvconf so maybe this is a conflict between resolvconf and NetworkManager not in 'use resolvconf' mode.